It is known to print letters or other devices on to the surface of a substrate of plastics material by hot foil printing. In this known arrangement, the substrate is moved along by transfer means to a workstation at which a printing tape having printing material thereon is compressed between the surface of the substrate and a heated die. The heated die has a print pattern in the form of letters or other devices formed in reverse thereon. On compression of the printing tape, the printing material is transferred from the printing tape to the surface of the substrate to form the letters or other devices thereon. It has been found that small blemishes (for example, depressions as small as 0.01 mm) in the surface of the substrate can seriously affect the quality of the print.